G0MRF's Laser equipment at Fairlight
David Bowman G0MRF and myself (Allan Wyatt G8LSD) have conducted tests over the last four months with Derek Atter G3GRO and Lech Laszkiewicz G3KAU. The distances have developed from a few tens of metres to 20 km, then 40 km and finally on Saturday, 5th April,2003 to 49.3 km. The path being from Fairlight east of Hastings to Capel le Ferne east of folkestone. The distance was verified by using the G4JNT software.
Semiconductor lasers operating at 670nM were used at both ends: 3mW to a beam expander at the G8LSD end, and 10mW 'barefoot' at the G0MRF end. Both receivers were designed independently and operated at audio baseband without a carrier. 488Hz tones were generated in the transmitters for modulating the lasers by the dividing down of a crystal oscillator. Keying of the tone providing the CW. Both receivers featured audio filters to reduce bandwidth. I used a TimeWave DSP filter and David used a home brew op-amp based filter peaking on 488Hz
With the 40km path showing very significant scintillation of the signal, we had also taken laptop computers so that very slow CW could be sent and received to overcome any scintillation. In the event the audio was clear enough to read without additional aids.
Each station had separate RX and TX equipment. G0MRF used a purpose built telescope around a 100mm lens to gather light on receive and I used a Russian 4.5 inch reflector telescope and swapped the eyepiece for the detector head. Both transmitters used tripod bases with vernier adjustments mounted above. Finally the transmitter mounted on the vernier mechanism. Aiming of the laser was by rifle sight secured to the TX housing. Strong and very cold winds worked against long term holding of the beam position, but even when the laser dimmed from the brightest light in the sky to only just visible with binoculars, the signal remained audible.
We arrived on site at 18:30 UTC and saw a good sunset but no view, it was quite misty. The power station at Dungeness some 30 km away disappeared completely by 19:00 UTC. By 21:25 we had a sighting of the powerful white lights used for aiming as a dim yellow disc. The laser was aimed at the disk and at 21:30 the laser was switched on. G0MRF received the signal immediately and within a few minutes we had both systems aligned. Reports of 559 and 579 as well as both callsigns and additional characters were exchanged by 21:45.
In spite of wearing fleece lined trousers, a sweatshirt, two fleeces and a cagoule, as well as walking boots, it took me several hours to warm up after the event.
My long suffering wife, (daughter of G3JMB) and I celebrated 29 years of marriage the following day. On the way home on Saturday, at just after midnight, she expressed that she had been engaged in some daft radio expeditions in her life but nothing so stupid as standing on a clifftop in a bitingly cold wind in the pitch dark for three hours.
Updated 18 OCT 2003